diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 1425b8c2ac..80aa70cd39 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -17,8 +17,8 @@ jobs:
     runs-on: ubuntu-24.04
     strategy:
       matrix:
-        elixir: [1.19.2]
-        otp: [28.1]
+        elixir: [1.20.1]
+        otp: [29.0]
 
     steps:
       - name: Checkout code
@@ -76,8 +76,6 @@ jobs:
     strategy:
       matrix:
         include:
-          - elixir: '1.15.0'
-            otp: '26.0'
           - elixir: '1.16.0'
             otp: '26.2'
           - elixir: '1.17.0'
@@ -86,6 +84,8 @@ jobs:
             otp: '27.2'
           - elixir: '1.19.2'
             otp: '28.1'
+          - elixir: '1.20.1'
+            otp: '29.0'
 
     steps:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd
@@ -121,4 +121,3 @@ jobs:
 
       - name: Run Checks
         run: bin/ci.sh
-
diff --git a/README.md b/README.md
index 57ae0c072c..7c933612b8 100644
--- a/README.md
+++ b/README.md
@@ -8,7 +8,7 @@
 
 ## Setup
 
-The exercises currently target Elixir versions from 1.15 to 1.19 and Erlang/OTP versions from 25 to 27. Detailed installation instructions can be found at
+The exercises currently target Elixir versions from 1.16 to 1.20 and Erlang/OTP versions from 26 to 29. Detailed installation instructions can be found at
 [https://elixir-lang.org/install.html](https://elixir-lang.org/install.html). We recommend using the [asdf version manager](https://github.com/asdf-vm/asdf) to manage multiple Elixir versions.
 
 ## Testing
diff --git a/exercises/concept/city-office/test/form_test.exs b/exercises/concept/city-office/test/form_test.exs
index 0f9623abe4..ce9f809f08 100644
--- a/exercises/concept/city-office/test/form_test.exs
+++ b/exercises/concept/city-office/test/form_test.exs
@@ -76,7 +76,7 @@ defmodule FormTest do
     end
   end
 
-  defmacrop assert_type({module_name, type_name}, expected_type_definition) do
+  defmacrop assert_type({module_name, type_name}, expected_type_definitions) do
     quote do
       {:ok, types} = Code.Typespec.fetch_types(unquote(module_name))
 
@@ -94,15 +94,11 @@ defmodule FormTest do
 
       actual_type_definition = Macro.to_string(type_definition)
 
-      if is_list(unquote(expected_type_definition)) do
-        if actual_type_definition in unquote(expected_type_definition) do
-          assert true
-        else
-          # we know this will fail at this point, but we're using it to provide a nice failure message
-          assert actual_type_definition == hd(unquote(expected_type_definition))
-        end
+      if actual_type_definition in unquote(expected_type_definitions) do
+        assert true
       else
-        assert actual_type_definition == unquote(expected_type_definition)
+        # we know this will fail at this point, but we're using it to provide a nice failure message
+        assert actual_type_definition == hd(unquote(expected_type_definitions))
       end
     end
   end
@@ -231,10 +227,10 @@ defmodule FormTest do
 
     @tag task_id: 5
     test "has a custom 'address_tuple' type with named arguments" do
-      expected_type_definition =
-        "{street :: String.t(), postal_code :: String.t(), city :: String.t()}"
+      expected_type_definitions =
+        ["{street :: String.t(), postal_code :: String.t(), city :: String.t()}"]
 
-      assert_type({Form, :address_tuple}, expected_type_definition)
+      assert_type({Form, :address_tuple}, expected_type_definitions)
     end
 
     @tag task_id: 5
diff --git a/exercises/concept/kitchen-calculator/test/kitchen_calculator_test.exs b/exercises/concept/kitchen-calculator/test/kitchen_calculator_test.exs
index 331cbb4e5e..7363b088a8 100644
--- a/exercises/concept/kitchen-calculator/test/kitchen_calculator_test.exs
+++ b/exercises/concept/kitchen-calculator/test/kitchen_calculator_test.exs
@@ -88,22 +88,22 @@ defmodule KitchenCalculatorTest do
   describe "convert from x to y:" do
     @tag task_id: 4
     test "teaspoon to tablespoon" do
-      assert KitchenCalculator.convert({:teaspoon, 15}, :tablespoon) == {:tablespoon, 5}
+      assert KitchenCalculator.convert({:teaspoon, 15}, :tablespoon) == {:tablespoon, 5.0}
     end
 
     @tag task_id: 4
     test "cups to fluid ounces" do
-      assert KitchenCalculator.convert({:cup, 4}, :fluid_ounce) == {:fluid_ounce, 32}
+      assert KitchenCalculator.convert({:cup, 4}, :fluid_ounce) == {:fluid_ounce, 32.0}
     end
 
     @tag task_id: 4
     test "fluid ounces to teaspoons" do
-      assert KitchenCalculator.convert({:fluid_ounce, 4}, :teaspoon) == {:teaspoon, 24}
+      assert KitchenCalculator.convert({:fluid_ounce, 4}, :teaspoon) == {:teaspoon, 24.0}
     end
 
     @tag task_id: 4
     test "tablespoons to cups" do
-      assert KitchenCalculator.convert({:tablespoon, 320}, :cup) == {:cup, 20}
+      assert KitchenCalculator.convert({:tablespoon, 320}, :cup) == {:cup, 20.0}
     end
   end
 end
diff --git a/exercises/concept/paint-by-number/.meta/exemplar.ex b/exercises/concept/paint-by-number/.meta/exemplar.ex
index 145139a7d2..875bd8a4d8 100644
--- a/exercises/concept/paint-by-number/.meta/exemplar.ex
+++ b/exercises/concept/paint-by-number/.meta/exemplar.ex
@@ -30,7 +30,7 @@ defmodule PaintByNumber do
 
     case picture do
       <<>> -> nil
-      <<pixel_color_index::size(palette_bit_size), _::bitstring>> -> pixel_color_index
+      <<pixel_color_index::size(^palette_bit_size), _::bitstring>> -> pixel_color_index
     end
   end
 
@@ -39,7 +39,7 @@ defmodule PaintByNumber do
 
     case picture do
       <<>> -> <<>>
-      <<_::size(palette_bit_size), rest::bitstring>> -> rest
+      <<_::size(^palette_bit_size), rest::bitstring>> -> rest
     end
   end
 
diff --git a/exercises/concept/top-secret/test/top_secret_test.exs b/exercises/concept/top-secret/test/top_secret_test.exs
index 82c9687a07..d3cdd64ebb 100644
--- a/exercises/concept/top-secret/test/top_secret_test.exs
+++ b/exercises/concept/top-secret/test/top_secret_test.exs
@@ -1,13 +1,16 @@
 defmodule TopSecretTest do
   use ExUnit.Case
 
+  # Maintainer notes:
+  # - in Elixir 1.17, `:...` got [] as an argument list, before that it was nil
+  # - in Elixir 1.20, `:__block__` got the line number in the metadata, before that it was empty
+
   describe "to_ast/1" do
     @tag task_id: 1
     test "handles an empty string" do
       string = ""
-      ast = {:__block__, [], []}
 
-      assert TopSecret.to_ast(string) == ast
+      assert {:__block__, _line_1_or_empty_list, []} = TopSecret.to_ast(string)
     end
 
     @tag task_id: 1
@@ -17,14 +20,12 @@ defmodule TopSecretTest do
       y = x - 2
       """
 
-      ast =
-        {:__block__, [],
-         [
-           {:=, [line: 1], [{:x, [line: 1], nil}, 7]},
-           {:=, [line: 2], [{:y, [line: 2], nil}, {:-, [line: 2], [{:x, [line: 2], nil}, 2]}]}
-         ]}
-
-      assert TopSecret.to_ast(string) == ast
+      assert {:__block__, _line_1_or_empty_list,
+              [
+                {:=, [line: 1], [{:x, [line: 1], nil}, 7]},
+                {:=, [line: 2],
+                 [{:y, [line: 2], nil}, {:-, [line: 2], [{:x, [line: 2], nil}, 2]}]}
+              ]} = TopSecret.to_ast(string)
     end
 
     @tag task_id: 1
@@ -45,7 +46,7 @@ defmodule TopSecretTest do
                  [
                    do: {
                      :__block__,
-                     [],
+                     _line_1_or_empty_list,
                      [
                        {:@, [line: 2],
                         [
diff --git a/exercises/practice/beer-song/test/beer_song_test.exs b/exercises/practice/beer-song/test/beer_song_test.exs
index 2c6d0f4f3e..0ce5ce2fc9 100644
--- a/exercises/practice/beer-song/test/beer_song_test.exs
+++ b/exercises/practice/beer-song/test/beer_song_test.exs
@@ -46,7 +46,7 @@ defmodule BeerSongTest do
   describe "lyrics" do
     @tag :pending
     test "first two verses" do
-      assert BeerSong.lyrics(99..98) == """
+      assert BeerSong.lyrics(99..98//-1) == """
              99 bottles of beer on the wall, 99 bottles of beer.
              Take one down and pass it around, 98 bottles of beer on the wall.
 
@@ -57,7 +57,7 @@ defmodule BeerSongTest do
 
     @tag :pending
     test "last three verses" do
-      assert BeerSong.lyrics(2..0) == """
+      assert BeerSong.lyrics(2..0//-1) == """
              2 bottles of beer on the wall, 2 bottles of beer.
              Take one down and pass it around, 1 bottle of beer on the wall.
 
diff --git a/exercises/practice/collatz-conjecture/test/collatz_conjecture_test.exs b/exercises/practice/collatz-conjecture/test/collatz_conjecture_test.exs
index 5ae629868e..22e83d52b2 100644
--- a/exercises/practice/collatz-conjecture/test/collatz_conjecture_test.exs
+++ b/exercises/practice/collatz-conjecture/test/collatz_conjecture_test.exs
@@ -39,9 +39,4 @@ defmodule CollatzConjectureTest do
   test "negative value is an error " do
     assert_raise FunctionClauseError, fn -> CollatzConjecture.calc(-15) end
   end
-
-  @tag :pending
-  test "string as input value is an error " do
-    assert_raise FunctionClauseError, fn -> CollatzConjecture.calc("fubar") end
-  end
 end
diff --git a/exercises/practice/intergalactic-transmission/.meta/example.ex b/exercises/practice/intergalactic-transmission/.meta/example.ex
index b905f6ad1a..0a6fe05678 100644
--- a/exercises/practice/intergalactic-transmission/.meta/example.ex
+++ b/exercises/practice/intergalactic-transmission/.meta/example.ex
@@ -29,7 +29,7 @@ defmodule Transmission do
   @spec get_parity(bitstring()) :: <<_::1>>
   defp get_parity(data) do
     bit_count = bit_size(data)
-    <<value::size(bit_count)>> = data
+    <<value::size(^bit_count)>> = data
 
     parity_int =
       0..(bit_count - 1)
@@ -71,7 +71,7 @@ defmodule Transmission do
 
   defp finalize(data, acc) when bit_size(data) == 7 do
     bits_count = 8 - rem(bit_size(acc), 8)
-    <<head::size(bits_count), _::bitstring>> = data
+    <<head::size(^bits_count), _::bitstring>> = data
     <<acc::bitstring, head::size(bits_count)>>
   end
 end
diff --git a/exercises/practice/kindergarten-garden/.meta/example.ex b/exercises/practice/kindergarten-garden/.meta/example.ex
index 3d4db7bd37..321994ce10 100644
--- a/exercises/practice/kindergarten-garden/.meta/example.ex
+++ b/exercises/practice/kindergarten-garden/.meta/example.ex
@@ -51,8 +51,8 @@ defmodule Garden do
     letters = "#{first_row_letters}#{second_row_letters}"
     map = add_to_map(map, current_name, letters)
 
-    first_row = String.slice(first_row, 2..-1//-1)
-    second_row = String.slice(second_row, 2..-1//-1)
+    first_row = String.slice(first_row, 2..-1//1)
+    second_row = String.slice(second_row, 2..-1//1)
     populate_map(first_row, second_row, map, student_names)
   end
 
diff --git a/exercises/practice/list-ops/test/list_ops_test.exs b/exercises/practice/list-ops/test/list_ops_test.exs
index e226fe4350..2ef7ce0502 100644
--- a/exercises/practice/list-ops/test/list_ops_test.exs
+++ b/exercises/practice/list-ops/test/list_ops_test.exs
@@ -42,7 +42,7 @@ defmodule ListOpsTest do
     @tag :pending
     @tag :slow
     test "huge list" do
-      assert L.reverse(Enum.to_list(1..1_000_000)) == Enum.to_list(1_000_000..1)
+      assert L.reverse(Enum.to_list(1..1_000_000)) == Enum.to_list(1_000_000..1//-1)
     end
   end
 
diff --git a/exercises/practice/pascals-triangle/.meta/example.ex b/exercises/practice/pascals-triangle/.meta/example.ex
index f824b1a702..d67fcf2b01 100644
--- a/exercises/practice/pascals-triangle/.meta/example.ex
+++ b/exercises/practice/pascals-triangle/.meta/example.ex
@@ -24,7 +24,7 @@ defmodule PascalsTriangle do
   defp each_cons(list) do
     list
     |> Enum.flat_map(&[&1, &1])
-    |> Enum.slice(1..-2//-1)
+    |> Enum.slice(1..-2//1)
     |> Enum.chunk_every(2)
   end
 
diff --git a/exercises/practice/pig-latin/.meta/example.ex b/exercises/practice/pig-latin/.meta/example.ex
index de9fd96335..ccc0d343e2 100644
--- a/exercises/practice/pig-latin/.meta/example.ex
+++ b/exercises/practice/pig-latin/.meta/example.ex
@@ -54,6 +54,6 @@ defmodule PigLatin do
   end
 
   defp move_prefix_to_the_end(string, prefix) do
-    String.slice(string, String.length(prefix)..-1) <> prefix
+    String.slice(string, String.length(prefix)..-1//1) <> prefix
   end
 end
diff --git a/exercises/practice/rail-fence-cipher/.meta/example.ex b/exercises/practice/rail-fence-cipher/.meta/example.ex
index 60d080ddbc..afa0d17d25 100644
--- a/exercises/practice/rail-fence-cipher/.meta/example.ex
+++ b/exercises/practice/rail-fence-cipher/.meta/example.ex
@@ -16,17 +16,18 @@ defmodule RailFenceCipher do
   Decode a given rail fence ciphertext to the corresponding plaintext
   """
   @spec decode(String.t(), pos_integer) :: String.t()
+  def decode("", _), do: ""
   def decode(str, 1), do: str
 
   def decode(str, rails) do
-    0..(String.length(str) - 1)
+    0..(String.length(str) - 1)//1
     |> Enum.to_list()
     |> fill_fence(rails)
     |> extract_original(str)
   end
 
   defp extract_original(fence, str) do
-    0..(String.length(str) - 1)
+    0..(String.length(str) - 1)//1
     |> Enum.map(fn i ->
       String.at(str, Enum.find_index(fence, &(&1 == i)))
     end)
@@ -34,7 +35,8 @@ defmodule RailFenceCipher do
   end
 
   defp fill_fence(list_chars, rails) do
-    rail_zigzag_indexes = Enum.concat(Enum.to_list(0..(rails - 1)), Enum.to_list((rails - 2)..1))
+    rail_zigzag_indexes =
+      Enum.concat(Enum.to_list(0..(rails - 1)//1), Enum.to_list((rails - 2)..1//-1))
 
     create_empty_fence(rails, length(list_chars))
     |> set_chars_to_fence(list_chars, rail_zigzag_indexes)
diff --git a/exercises/practice/two-fer/test/two_fer_test.exs b/exercises/practice/two-fer/test/two_fer_test.exs
index 86380254b5..5bf38ccf8e 100644
--- a/exercises/practice/two-fer/test/two_fer_test.exs
+++ b/exercises/practice/two-fer/test/two_fer_test.exs
@@ -14,25 +14,4 @@ defmodule TwoFerTest do
   test "another name given" do
     assert TwoFer.two_fer("Bob") == "One for Bob, one for me."
   end
-
-  @tag :pending
-  test "when the argument is a number" do
-    assert_raise FunctionClauseError, fn ->
-      TwoFer.two_fer(10)
-    end
-  end
-
-  @tag :pending
-  test "when the argument is an atom" do
-    assert_raise FunctionClauseError, fn ->
-      TwoFer.two_fer(:bob)
-    end
-  end
-
-  @tag :pending
-  test "when the argument is a charlist" do
-    assert_raise FunctionClauseError, fn ->
-      refute TwoFer.two_fer(~c"Jon Snow")
-    end
-  end
 end